Comparison and Analysis of Heat Transfer and Inflow Rate for Supercritical Carbon Dioxide Based on Different Tubes

This paper is twofold. First, the effect of non-linear thermophysical property variation was presented using supercritical carbon dioxide (SCO₂) around the thermodynamic pivotal point. The second part exhibits an experimental examination of the heat transfer (HT) behaviour of SCO₂ in a helical tube with a hydraulic diameter of 2 mm at different mass fluxes (MF), heat fluxes (HF), and pressures (P). The experiments were carried out based on various pressures, mass fluxes, and heat fluxes for both scenarios. CO₂ was cooled in a 2 mm diameter serpentine tube made of copper material. The experimental results showed that HT degradation could happen under the circumstances of a change in HF and MF and have significant effects on fluid inflow and HT performance. Also, buoyancy plays an essential and influential role in the HT factors. By increasing the pressure value, the HT parameters decrease when the pressure reaches 8 MPa, and the flotation value is more significant, which means a decrease in the HT factor. Finally, under the system circumstances, the HT value decreases with the increase in heat flux and pressure and increases with the increment in MF.